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Update installation guide
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166
INSTALLATION.md
166
INSTALLATION.md
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@ -62,18 +62,6 @@ btrfs subvolume create /mnt/nix
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btrfs subvolume create /mnt/log
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btrfs subvolume create /mnt/persist
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btrfs subvolume create /mnt/data
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```
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We will now take a read-only snapshot of the root subvolume.
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This snapshot will be eventually used for rolling back to on every boot (impermanence).
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```shell
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btrfs subvolume snapshot -r /mnt/root /mnt/root-blank
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```
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And finally, we can unmount the btrfs root.
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```shell
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umount /mnt
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```
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@ -226,7 +214,11 @@ fileSystems."/" =
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### Subvolumes needed for boot
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In order to correctly persist `/var/log`, the respective subvolume need to be mounted early enough in
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the boot process. To do this, we will want to add `neededForBoot = true;`, so the entry will look like this:
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the boot process. To do this, we will want to add `neededForBoot = true;`. Additionally, we will also
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need to add this parameter for our `/persisr` subvolume. This is because we will be storing the user
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password (including root password) in a password file there (mentioned later on).
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So the entries will look like this:
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```nix
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fileSystems."/var/log" =
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@ -235,10 +227,14 @@ fileSystems."/var/log" =
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options = [ "subvol=log" "noatime" "compress=zstd:3" ];
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neededForBoot = true;
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};
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```
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Additionally, we will also need to add `neededForBoot = true;` to our `/persist` subvolume. This is because
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we will be storing the root users password file in there.
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fileSystems."/persist" =
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{ device = "/dev/disk/by-label/NIXFS";
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fsType = "btrfs";
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options = [ "subvol=persist" "noatime" "compress=zstd:3" ];
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neededForBoot = true;
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};
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```
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## Minimal config
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@ -310,12 +306,11 @@ screen. Log in as root, set your password (`passwd itsdrike`), log out and re-lo
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This is an optional step, if you don't want your root partition to get auto-reset on each boot, you can simply skip this.
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### Auto-restore root-blank snapshot
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### Auto-wipe root partition
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Remember how we create the empty snapshot of our root subvolume? Well now comes the time when we put it to use. We will
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restore this snapshot from initrd, which runs in a temporary file-system, before our actual file-system is even mounted.
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This makes it a perfect place to run a script which will restore our root subvolume to the blank snapshot before each
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boot.
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To reset the root subvolume on every boot, we can simply delete it and create a new one in its place. We will be doing
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this from initrd, which runs in a temporary file-system, before the actual file-system is properly mounted (following
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fstab). This makes it a perfect place to run a script, which will wipe the root subvolume before each boot.
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I will set this up using a systemd-based initrd, because I will need systemd for TPM unlocking later on. If you don't
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care about that, it is also possible to do this without systemd. You can a guide for such setup
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@ -338,41 +333,37 @@ boot.initrd.systemd = {
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unitConfig.DefaultDependencies = "no";
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serviceConfig.Type = "oneshot";
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script = ''
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mkdir -p /mnt
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# Mount the BTRFS root to /mnt so we can manipulate btrfs subvolumes
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mount --mkdir /dev/mapper/cryptfs /mnt
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# We first mount the btrfs root to /mnt
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# so we can manipulate btrfs subvolumes.
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mount /dev/mapper/cryptfs /mnt
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# While we're tempted to just delete /root and create
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# a new snapshot from /root-blank, /root is already
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# populated at this point with a number of subvolumes,
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# which makes `btrfs subvolume delete` fail.
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# So, we remove them first.
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# Simply deleting a subvolume with btrfs subvolume delete will not work,
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# if that subvolume contains other btrfs subvolumes. Because of that, we
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# instead use this function to delete subvolumes, whihc will first perform
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# a recursive deletion of any nested subvolumes.
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#
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# /root contains subvolumes:
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# - /root/var/lib/portables
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# - /root/var/lib/machines
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#
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# These are probably related to systemd-nspawn, but
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# since I don't use it, I'm not 100% sure.
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# Anyhow, deleting these subvolumes hasn't resulted in
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# any issues so far, except for fairly benign-looking
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# errors from systemd-tmpfiles.
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btrfs subvolume list -o /mnt/root |
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cut -f9 -d' ' |
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while read subvolume; do
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echo "deleting /$subvolume subvolume..."
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btrfs subvolume delete "/mnt/$subvolume"
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done &&
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echo "deleting /root subvolume..." &&
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btrfs subvolume delete /mnt/root
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# This is necessary, because the root subvolume will actually usually contain
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# other subvolumes, even if the user haven't created those explicitly. It seems
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# that NixOS creates these automatically. Namely, I observed these in root subvol:
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# - root/srv
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# - root/var/lib/portables
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# - root/var/lib/machines
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# - root/var/tmp
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delete_subvolume_recursively() {
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IFS=$'\n'
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for x in $(btrfs subvolume list -o "$1" | cut -f 9- -d ' '); do
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delete_subvolume_recursively "/mnt/$x"
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done
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echo "restoring blank /root subvolume..."
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btrfs subvolume snapshot /mnt/root-blank /mnt/root
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echo "Deleting subvolume $1"
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btrfs subvolume delete "$1"
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}
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# Once we're done rolling back to a blank snapshot,
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# we can unmount /mnt and continue on the boot process.
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# Recreate the root subvolume
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delete_subvolume_recursively "/mnt/root"
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echo "Re-creating root subvolume"
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btrfs subvolume create "/mnt/root"
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# we can now unmount /mnt and continue on the boot process.
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umount /mnt
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'';
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};
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@ -407,12 +398,6 @@ in
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];
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files = [
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"/etc/machine-id"
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# ssh stuff
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"/etc/ssh/ssh_host_ed25519_key"
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"/etc/ssh/ssh_host_ed25519_key.pub"
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"/etc/ssh/ssh_host_rsa_key"
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"/etc/ssh/ssh_host_rsa_key.pub"
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];
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};
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@ -422,6 +407,21 @@ in
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"L /var/lib/NetworkManager/seen-bssids - - - - /persist/system/var/lib/NetworkManager/seen-bssids"
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"L /var/lib/NetworkManager/timestamps - - - - /persist/system/var/lib/NetworkManager/timestamps"
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];
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# Define host key paths in the persistent mount point instead of using impermanence for these.
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# This works better, because these keys also get auto-created if they don't already exist.
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services.openssh.hostKeys = mkForce [
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{
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bits = 4096;
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path = "/persist/system/etc/ssh/ssh_host_rsa_key";
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type = "rsa";
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}
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{
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bits = 4096;
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path = "/persist/system/etc/ssh/ssh_host_ed25519_key";
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type = "ed25519";
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}
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];
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}
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```
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@ -436,23 +436,25 @@ Note that with impermanence, your user passwords will get erased too (with the `
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you can create password files, which will contain the password hashes for each user:
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```shell
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mkpasswd -m sha-512 > /persist/system/passwords/root
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mkpasswd -m sha-512 > /persist/system/passwords/itsdrike
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mkdir -p /persist/passwords
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chmod 700 /persist/passwords
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mkpasswd -m sha-512 > /persist/passwords/root
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mkpasswd -m sha-512 > /persist/passwords/itsdrike
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chmod 600 /persist/passwords/*
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```
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And declare these in our `configuration.nix` or `impermanence.nix`
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```nix
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users = {
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# This option makes it that users are not mutable outside our configuration
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# If you are using impermanence, this will actually be the case regardless of this setting,
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# however, setting this explicitly is a good idea, because nix will warn us if
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# our users don't have passwords set
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# This option makes it that users are not mutable outside of our configuration.
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# If you're using root impermanence, this will actually be the case regardless
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# of this setting, however, setting this explicitly is a good idea, because nix
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# will warn us if our users don't have passwords set, preventing lock outs.
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mutableUsers = false;
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# Each existing user needs to have a password file defined here
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# otherwise, they will not be available to login.
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# These password files can be generated using the following command:
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# Each existing user needs to have a password file defined here, otherwise
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# they will not be available to login. These password files can be generated with:
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# mkpasswd -m sha-512 > /persist/passwords/myuser
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users = {
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root = {
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@ -601,7 +603,6 @@ The resulting file should then look something like this:
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{
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imports = [
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./hardware-configuration.nix
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./impermanence.nix
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];
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boot.supportedFilesystems = [ "btrfs" ];
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@ -625,6 +626,21 @@ The resulting file should then look something like this:
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system = {
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hostname = "anduril";
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username = "itsdrike";
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impermanence = {
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root = {
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enable = true;
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# Some people use /nix/persist/system for this, leaving persistent files in /nix subvolume
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# I much prefer using a standalone subvolume for this though.
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persistentMountPoint = "/persist";
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};
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# Configure automatic root subvolume wiping on boot from initrd
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autoWipeBtrfs = {
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enable = true;
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devices."/dev/disk/by-label/NIXROOT".subvolumes = [ "root" ];
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};
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};
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};
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device = {
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virtual-machine = false;
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@ -646,12 +662,14 @@ The resulting file should then look something like this:
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}
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```
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> [!WARNING]
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> I'm currently working on making impermanence config in my flake directly. This will mean you will eventually be
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> expected to just enable impermanence through myOptions. Right now, the config above includes `impermanence.nix`
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> that we have enabled earlier. This will work, however note that flakes are a bit stricter with fetchTarball, and
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> require a sha256 hash to be specified. You can specify it, or use the `--impure` flag for now. Once impermanence
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> will be integrated into my flake, it will be handled as an input, and you won't have to worry about anything.
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> [!NOTE]
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> You may notice that this configuration also includes custom options for impermanence,
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> and that the impermanence.nix is no longer declared in imports. This is because my
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> flake already contains a fully custom support (mostly similar to what I've shown here)
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> to handle impermanence. This allows me to re-use this impermanence across multiple
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> machines very easily.
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>
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> You can now therefore delete the `impermanence.nix` file.
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### Commit and switch
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